DNA Structure and Function

Review!

•Nucleus : “brain” of the cell.

•Chromosomes: found in the nucleus.

DNA BIG Picture• Chromosomes are made of DNA.• DNA has your genes on it.• DNA has the instructions for making

all proteins for the organism.• DNA is unique to each individual.• DNA determines how an organism

looks and functions (traits).• Each human has about 30,000 genes

on the DNA.

DNA

Deoxyribonucleic acid

Located in the nucleus of a cell.

Is a type of nucleic acid.

Made up of repeating nucleotide subunits.

DNA Codes for Proteins

• All living things contain proteins. Proteins are essential to all of life.

• ENZYMES ARE PROTEINS!!• Enzymes control all the chemical reactions in an

organism and are extremely important molecules in biology.

• DNA contains all of the information needed to build all of the proteins for our bodies.

1 nucleotide looks like:

Phosphate Group

Deoxyribose Sugar

NitrogenousBase

4 types: Adenine (A)

Guanine (G)

Cytosine (C)

Thymine (T)

2 strands so bases can pair upA binds T onlyC binds G only

P

S

P

S

A

C

Strand 1

P

S

P

S

T

G

Strand 2

Phosphates + sugars on the outside

Bases on the inside (Bases fit like puzzle pieces)

Remember

DNA is like an Oreo

Phosphates + sugars = cookiesBases = cream filling

BASE PAIRING RULES

What holds DNA together?

A T have two hydrogen bonds

P

S

P

S

A

C

Strand 1

P

S

P

S

T

G

Strand 2

G C have three hydrogen bonds

• Two strands of nucleotides twist together double helix

James Watson and Francis Crick discovered the double helix structure (They won the Nobel Prize)

How does DNA carry information?

• DNA carries information in the form of nucleotide sequences.

• For example: – The sequence ATATGCTCTA carries different

information from the sequence CGGTATTAAC.

• Different combinations of the same 4 nucleotides creates a near infinite number of unique genes.

DNA is complementary

Bases on one strand match up with the bases on the other strand (A-T and G-C)

Example: Strand 1- ATG GGC CTA Strand 2- TAC CCG GAT

DNA Replication During cell division

(interphase), chromosomes replicate to form exact copies to pass along to daughter cells.

That means the DNA replicates!

The DNA unzips and 2 new strands form.

A complete, exact copy of DNA is created.

Each side serve as a template for the other side (called semi-conservative replication).

DNA never ever leaves the nucleus

• DNA is the master copy of the directions a cell needs to live so it needs to be protected

DNA in the

nucleus is safe

But DNA in the

cytoplasm can be

destroyed

RNA

• Ribonucleic Acid

• Building Blocks:nucleotides

• A nucleotide is:– A sugar (ribose)*– A phosphate – A nitrogen base

• RNA has 4 nitrogen Bases (just like DNA)

– Adenine– Guanine– Cytocine– Uracil **

RNA is only a single strand***

Three types of RNA****• Messenger RNA (mRNA)-

copies info from DNA and takes the message to the cytoplasm.

• Ribosomal RNA (rRNA)- makes up ribosomes, assembles proteins.

• Transfer RNA (tRNA)- transfers amino acids to the ribosomes to become proteins.

Protein Synthesis Overview

• Protein synthesis occurs in two steps:

1. Transcription

2. Translation

ScribesScripts

Copy script for actors

Transcription• Definition: RNA is made from 1 gene in

DNA• The type of RNA made is called mRNA

(messenger RNA) because it sends a message from DNA to the cytoplasm

DNA safe in the nucleus

Uses mRNATo send a

message to the cytoplasm

Transcription Enzymes unzip one gene in DNA Match up bases to one side of a

gene in DNA mRNA detaches from the DNA,

DNA joins back together mRNA moves out of the nucleus

and into the cytoplasm

•DNA: GAG AAC TAG TAC•RNA: CUC UUG AUC AUG

For figuring out RNA:A binds UC binds G

How does mRNA tell the cell what to do?

• mRNA is a message that codes for a protein

• Proteins are made in the cytoplasm (at the – ribosomes)

• Translation (protein synthesis): Process of making a protein

• Proteins are made up of amino acids (small building blocks) -There are 20 different types of amino acids

Amino Acids

Protein

Transcription happens in the nucleus. An RNA copy of a gene is

made.

Then the mRNA that has been

made moves out of the

nucleus into the

cytoplasm

Once in the cytoplasm,

the mRNA is used to make

a protein

Cytoplasm of cell

Nucleus

DNAmRNA mRNA

TranslationTranslation

Ribosome reads the mRNA and puts together protein

“Translating mRNA into protein”

Cytoplasm

Nucleus

Ribosome

Process of Translation

1. mRNA moves out of nucleus

through nuclear pore

and into cytoplasm

2. mRNA attaches to a

ribosome

Cytoplasm

Nucleus

Ribosome

Process of Translation

3. Transfer RNA (tRNA) decodes the mRNA and brings

amino acids to build up the protein

tRNAAmino acid

Anticodon (3 bases on tRNA): Matches

up to codons on mRNA

Cytoplasm

Nucleus

Ribosome

Process of Translation

4. Protein (chain of amino acids) detaches from ribosome and goes off to work in the cell

Ribosome

tRNA Molecule

Polypeptide

¼ hemoglobin protein

Transfer RNA

(tRNA)Piece of RNA

Transfers 1 amino acid to protein being made at ribosome

Translation

RibosomeHelps line up the mRNA and tRNA

Part of the ribosome is actually made of RNA.

Can you guess what they are going to call this type of RNA?

rRNA

Translation

Genetic Code• Codon: group of 3 mRNA nitrogen bases

that code for a specific amino acid

DNA:GTT 3 NucleotidesCodon Chart

Amino acid: Gln

mRNA: CAA codon

tRNA: GUU anticodon

There are 64 codons that code for 20 amino acids

…43 = 64 different possible

codons

How is this possible? …. More than one codon

may code for an amino acid

The genetic code is said to be universal because it is the same in almost all organisms

Worm – AUG = methionine

Human – AUG = methionine

Example:CGU, CGC, CGA, CGG, AGA, & AGG

all code for arg

Central dogma of molecular biology

DNA RNA Protein

Directions to make proteins

are safely stored in the nucleus

Carries the directions to

the cytoplasm

Work to keep the cell alive

Transcription Translation

DNA: The Stuff of LifeDNA Structure and Gene Expression

While it might be hard to see, it’s in there, and it is in

every single cell of every living organism

on our planet.

What is the relationship between, chromosomes, DNA and genes?

All of the genetic information is stored in the nucleus of every cell in structures called “Chromosomes”

For humans, we have 23 pairs of chromosomes in virtually every cell in our body

Nucleotide Sequencing

The genetic code in DNA is based on the sequence of these letters.Each gene will

have a specific number of nucleotides/base pairs (length) and

sequence of letters.For example: Gene 1204-

B5Person A: ATTGCACGATAACGAPerson B: TCGATCAAACGCATA

Although they have same number of base pairs in the same gene, the sequence of

letters makes them different, thus a different version of that trait will be

expressed.

1. Use the ribosome sheet to create your own sentence. It must have at least 5 words and be school appropriate.

2. Write the mRNA sequence for your “protein.”

3. Write the DNA sequence for your “protein.”